Before we can answer why it is that we yawn, let’s talk about what a yawn is in the first place. Yawning is an involuntary action that causes our mouth to open wide and breathe in deeply. That air fills your lungs, causing your abdominal muscles to flex and the diaphragm to be pushed down. The yawn ends when you expel some of that air back out through your mouth. Research has shown that even fetuses yawn, proving that a yawn really is involuntary. So why do we yawn in the first place?

Why we yawn has been debated for centuries and some interesting theories have surfaced, attributing yawning to a lack of oxygen or of course, boredom and sleepiness.

The most recent research about yawning suggests that we yawn as a way to cool down our brain. A 2007 study done at the University of New York in Albany concluded that people yawned more in situations where their brain was more likely to be warmer. They performed their research by taking advantage of another curious phenomenon — contagious yawning. They asked participants to enter a room by themselves and watch videos of people behaving neutrally, laughing or yawning. Some participants were asked to breathe only through their nose or to press cool packs on their foreheads, both activities that cooled the brain. In those instances, contagious yawning was almost completely eliminated, leading to the conclusion that yawning works as a brain-cooling mechanism.

Which brings me to another question — why are yawns, unlike other reflexes, such as coughing or sneezing, contagious? Science has long believed that contagious yawning is a sign of empathy. There have been many studies done to support this theory. One in particular indicated that you are more likely to “catch a yawn” from someone the closer you feel to them — meaning you’d be more likely to catch a yawn from your hubby than from the lady behind you in the grocery store checkout line. Supporting this even further is research that shows that kids with autism (whose sense of empathy is impaired) aren’t able to “catch a yawn.” The difficulty may be linked to an impairment with the children’s mirror neurons, special brain cells that react when another person performs an action.

What’s interesting is that contagious yawning isn’t common in the animal kingdom, and that’s because most animals don’t have the same capacity for empathy that people do (except for chimpanzees). Dogs however, do yawn contagiously after their owners yawn, suggesting that their capacity to feel what a human is feeling is higher than that of other animals (a truth that many a dog owner will attest to).

Though yawning seems like a benign enough phenomenon, it turns out that excessive yawning can actually be a sign of heart attack or bleeding in and around your aorta (your heart’s main artery). If you are experiencing yawning coupled with other heart attack symptoms, like feeling like you have something heavy on your chest or shortness of breath, call 911 immediately. Of course, excessive yawning could also mean you’re just really tired. If you suspect that to be the case, try a nap.